JP7092666B2 - Pencil lead - Google Patents

Description

The present invention relates to a pencil lead in which the surface of the lead body is coated with a coating layer made of resin.

Pencil wicks are roughly classified into black wicks containing graphite as a main component and colored wicks in which pigments or dyes are added to the constitutional material as a coloring material. For the former, a firing process is indispensable in the manufacturing process. On the other hand, in the latter case, some are manufactured through such a firing step and some are not. The pencil lead manufactured through the firing step in this way exhibits a porous structure having innumerable fine pores (pores).
Colored wicks (so-called colored pencil wicks) manufactured by firing are mainly made of white or light-colored porous wicks, and then the pores are impregnated with dye ink. In the invention disclosed in Patent Document 1 below, the pores are filled with resin for the purpose of increasing the strength of the core body.

It is also possible to manufacture colored pencil leads in which pores are formed without undergoing a firing step, but the surface of such non-firing colored pencil leads is coated with an organic-inorganic hybrid material for the purpose of preventing deterioration over time due to moisture absorption. Also disclosed is a technique for forming a moisture-proof film (Patent Document 2 below).

Japanese Unexamined Patent Publication No. 2015-160878 JP-A-2002-348516.

Yoshiki Chujo, "Creation of Organic-Inorganic Nano Hybrid Material", Grinding, Hosokawa Powder Technology Laboratory Co., Ltd., October 30, 2006, No. 50, p. 11-15

In the above-mentioned Patent Document 2, the surface of the non-fired core is coated, but the idea of coating the fired core with a resin has never existed.
Therefore, it is an object of the present invention to further increase the mechanical strength of a pencil lead by coating the surface of the pencil lead manufactured through a firing step regardless of whether it is a black lead or a colored lead. ..

In view of the above problems, the pencil lead according to the present invention is a pencil lead in which the surface of the fired lead body is coated with a coating layer made of resin.
A pencil with the tip of the core left in a cylindrical shape and the tip of which is sharpened to a flat surface is pressed against the surface of a horizontal flat plate coated with the test resin with a thickness of 5 μm at a load of 7.355 N at a 45 ° angle. When the hardness of the pencil with the softest core that causes indentations on the surface when scratched is defined as the scratch hardness of the test resin,
The scratch hardness of the resin constituting the coating layer is HB or higher.

Here, the "pencil core" in the present invention is not only a normal pencil that is mounted in a wooden shaft, but also a pencil that is refillably mounted in a so-called lead holder and has a diameter of about 2 to 3 mm, or a so-called mechanical pencil. It also includes a pencil lead. Further, it does not matter whether the core is a black core or a colored core. Further, the main material thereof is graphite, boron nitride or the like, which is not particularly limited, but is formed through a firing step.
The "test resin" is a conceptual one for defining the scratch hardness, and the "resin" specifically used in the present invention is defined as such a "test resin" in the above definition. The scratch hardness is measured according to this.

Here, the test resin is specifically applied to a "thickness of 5 μm" by the method shown below.
That is, first, in order to make the test resin blend well with the brush, a part of the test resin is applied to a clean surface different from the test plate to adjust the condition of the brush and the mass of the brush in this state. Weigh. On the other hand, the amount required for the film pressure of the dried coating film of the test resin to reach 5 μm in a predetermined area is measured in advance. Then, the test resin and the required amount are accurately measured with a syringe, extruded onto the surface of the test plate, spread, and spread uniformly over the predetermined area with the brush. Whether or not the required amount of the test resin has been applied is confirmed by weighing the brush after application again and checking whether or not it is the same as the original mass.

The above-mentioned scratch hardness measurement is actually performed in accordance with JIS K 5600-5-4. Here, the above-mentioned load 7.355N corresponds to a weight of 750 g as the load specified in JIS K 5600-5-4.

The surface coated with the test resin is scratched with a pencil in the order of the soft core to the hard core as described above, and the test has the hardness of the pencil with the softest core among the pencils having indentations on the surface. It is defined as the "scratch hardness" of the resin. Then, the test resin having a scratch hardness of HB or more is used as the "resin" of the present invention, and this resin is applied to the surface of the pencil lead to form a "coating layer".

Even in a pencil lead having a coating layer formed of a resin having a scratch hardness of HB or higher and a thin coating having a surface of a fired core of about 1 μm or less, the scratch hardness is lower than that of a resin having a scratch hardness lower than that of HB. , Bending strength is improved. Further, when the pencil lead is a mechanical pencil lead, the holding force of the chuck that holds the lead is also improved. Here, the hardness indication "HB" of the pencil defined as the scratch hardness conforms to the hardness indication in Europe and Japan, which corresponds to "# 2" in the hardness indication in the United States.

Examples of such resins include organic-inorganic hybrid resins, polyolefin resins, vinyl resins, furan resins, ABS resins, phenol resins, ketone resins, maleic acid resins, acrylic resins, urea resins, urethane resins, epoxy resins, and silicone resins. It is desirable to be selected from the group consisting of, imide resin, amide resin and fluororesin.
Here, the "organic-inorganic hybrid resin" means "a combination of an inorganic material and an organic material", and "especially the mixture thereof is on the nano-order, sometimes on the molecular order". Such an organic-inorganic hybrid material is characterized by being "flexible like plastic but excellent in mechanical strength and heat resistance" (see Non-Patent Document 1 above).

The type of such an organic-inorganic hybrid resin is not particularly limited, but it is desirable to use a silica / organic hybrid resin. Here, the "silica-organic hybrid resin" refers to a hybrid resin made of silica as an inorganic material and an organic synthetic resin as an organic material. Specifically, commercially available products such as silica-epoxy hybrid resin, silica-phenol hybrid resin, silica-polyamic acid hybrid resin, silica-polyamide hybrid resin, and silica-acrylic hybrid resin can be used. However, it is particularly desirable to use a silica-epoxy hybrid resin from the viewpoint of the strength of the pencil lead after coating.

When the fired core is a colored core, it is desirable that the coating layer further contains a coloring material. As a result, for example, the color of the colored core can be displayed more clearly by the coating layer, and the design is enhanced. Of course, even when the fired core is a black core, the coating layer may be intentionally contained with a coloring material having a color different from black to enhance the design. Further, if a pigment is used as the coloring material, light resistance can be imparted to the core surface.

Further, if the coating layer further contains an ultraviolet absorber, it is possible to impart light resistance to the pencil lead.
Further, if the coating layer further contains an antistatic agent, it is possible to impart antistatic performance to the pencil lead.

According to the present invention, in a pencil lead manufactured through a firing step regardless of whether it is a black lead or a colored lead, the mechanical strength of the pencil lead can be further increased by coating the surface of the pencil lead with a resin. ..

The cross section of the core according to Example 2 was photographed with a scanning electron microscope.

(1) Boron Nitride Calcined Core A powdered boron nitride and a resin to be a binder are mixed (a plasticizer may be added as appropriate), and this compounding composition is kneaded. This kneaded product is extruded into fine lines. This molded product is heated and fired in an oxygen-free atmosphere such as in an inert gas to form a fired core of boron nitride and binder carbon. By heating and firing this fired core in an oxygen atmosphere, the binder carbon is oxidized and removed, and a porous fired core containing only boron nitride can be obtained. This porous fired core is white.

This white porous fired core is immersed in a liquid in which a coloring material and an organic solvent are mixed for a predetermined time, and the coloring material is contained in the pores. Then it is dried to remove the organic solvent.
Finally, the porous calcined core is immersed in oil and the pores are impregnated with the oil to complete the colored core. It should be noted that this oil can be used as long as it is generally used for impregnating the calcined core body such as liquid paraffin.

Then, the above-mentioned fired core is immersed in a liquid in which an organic-inorganic hybrid resin (particularly silica / organic hybrid resin) and an organic solvent are mixed for a predetermined time, and then dried to remove the organic solvent on the surface. Is coated with the resin. The coating with the resin may be carried out as a step between the step of containing the coloring material and the step of impregnating the oil as described above.

Here, depending on the thickness of the kneaded product when extruded, it is possible to form a colored lead as a pencil lead for a wooden shaft having a final diameter of about 2 to 3 mm and a replacement lead for a lead holder. It can also be formed as a replacement lead for mechanical pencils having a final diameter of 0.3 mm or more and 1 mm or less.
It is also possible to form the porous calcined core as a white core without containing a coloring material.

(2) Graphite calcined core Powder or scaly graphite and a resin to be a binder are mixed (a plasticizer may be added as appropriate), mixed and dispersed, and further kneaded. This kneaded product is extruded into fine lines. This molded product is heated and fired in an oxygen-free atmosphere such as in an inert gas to prepare a calcined core of graphite and binder carbon. This porous fired core is black. Then, the porous calcined core is immersed in oil, and the pores are impregnated with the oil to complete the black core. It should be noted that this oil can be used as long as it is generally used for impregnating the calcined core body such as liquid paraffin.

Then, the above-mentioned fired core is immersed in a liquid in which an organic-inorganic hybrid resin (particularly silica / organic hybrid resin) and an organic solvent are mixed for a predetermined time, and then dried to remove the organic solvent on the surface. Is coated with the resin. The coating with the resin may be carried out as a step between the step of containing the coloring material and the step of impregnating the oil as described above.

Here, depending on the thickness of the kneaded product when extruded, it is possible to form a black core as a pencil lead for a wooden shaft having a final diameter of about 2 to 3 mm and a replacement lead for a lead holder. It can also be formed as a replacement lead for mechanical pencils having a final diameter of 0.3 mm or more and 1 mm or less.

(1) Boron nitride calcined core The composition of the following composition is kneaded with a pressure kneader and two rolls, and this kneaded product is extruded into fine lines with an extruder in an inert gas (nitrogen gas) atmosphere. It was calcined at 1,000 ° C. for 5 hours to obtain a calcined core of boron nitride and binder carbon (hereinafter referred to as “BN core”).
Boron Nitride Powder: 50% by weight
Polyvinyl chloride resin (binder resin): 40% by weight
Dioctyl phthalate (plasticizer): 10% by weight

This BN core was further calcined at 700 ° C. for 12 hours in an atmospheric atmosphere to prepare a calcined core containing only boron nitride. This was impregnated with silicate 40 (corcoat), dried, and then calcined at 1,000 ° C. for 5 hours in an inert atmosphere to obtain a white calcined core.
The white calcined core was impregnated with a composition consisting of a coloring material having the following composition and an organic solvent, and dried at 80 ° C. for 12 hours.
Spiron Red C-PH (dye color material, Hodogaya Chemical): 20% by weight
Isopropyl alcohol (organic solvent): 80% by weight

The pores obtained by this drying were impregnated with α-olefin oil (Spectracin 4, ExxonMobil) at 100 ° C. for 6 hours to obtain a red mechanical pencil core having a diameter of 0.564 mm and a length of 60 mm. This red BN core was used as Examples 1 to 10 and Comparative Example 1 and Comparative Example 2 described later.

(2) Graphite calcined core The composition having the following composition was mixed and dispersed with a Henschel mixer, kneaded with a pressure kneader and two rolls, and the kneaded product was extruded into fine lines by an extruder. Then, the plasticizer is dried and removed, and further fired in an inert gas (nitrogen gas) atmosphere at 1,000 ° C. for 10 hours to obtain a black calcined core of graphite and binder carbon (hereinafter, “graphite core”). ".) Was obtained.
Scale-like natural graphite A: 40% by weight
Polyvinyl chloride resin (binder resin): 40% by weight
Sodium stearate (surfactant): 1% by weight
Dioctyl phthalate (plasticizer): 19% by weight

The scaly natural graphite A had an ab plane with a flatness of 0.2 μm, an mv value of 8 μm, a thickness of the c-axis of 1 μm, and an aspect ratio of 8.
This core was impregnated with α-olefin oil (Spectracin 4, ExxonMobil) at 100 ° C. for 6 hours to obtain a black mechanical pencil core having a diameter of 0.564 mm and a length of 60 mm. This graphite core was used as Example 11 and Comparative Example 3 described later.

(3) Example (3-1) Example 1
The BN core was immersed in a resin solution having the following composition, then taken out, and the solvent was dried to form a coating layer having a film thickness of about 1 μm on the surface.
Organic Inorganic Hybrid Resin (Composelan E203, Silica / Epoxy Hybrid Resin, Arakawa Chemical): 15% by weight
Organic solvent (isopropyl alcohol): 85% by weight
The scratch hardness of the coating film having a film thickness of 5 μm formed by the resin solution was 8H.

(3-2) Example 2
The BN core was immersed in a resin solution having the following composition, then taken out, and the solvent was dried to form a coating layer having a film thickness of about 1 μm on the surface. FIG. 1 shows a cross section of the core according to the second embodiment taken with a scanning electron microscope. In the figure, the portion of the BN core 10 having a blackish color tone appears to have a thin layer like a millefeuille, and it can be seen that the coating layer 10 having a whitish color tone is formed on the surface layer thereof. The thickness of the coating layer 20 is approximately 1.0 μm, although it varies depending on the site, when compared with the scale at the lower right in the figure. By the way, in other examples as well, a cross-sectional image as shown in the figure is generally confirmed.
Organic Inorganic Hybrid Resin (Composelan E203, Silica / Epoxy Hybrid Resin, Arakawa Chemical): 15% by weight
Pigment color material (MHI red, Mikuni color): 60% by weight
Organic solvent (isopropyl alcohol): 25% by weight
The scratch hardness of the coating film having a film thickness of 5 μm formed by the resin solution was 8H.

(3-3) Example 3
The BN core was immersed in a resin solution having the following composition, then taken out, and the solvent was dried to form a coating layer having a film thickness of about 1 μm on the surface.
Organic Inorganic Hybrid Resin (Composelan E203, Silica / Epoxy Hybrid Resin, Arakawa Chemical): 15% by weight
UV absorber (Hals Hybrid UV-G, Nippon Shokubai): 3% by weight
Organic solvent (isopropyl alcohol): 82% by weight
The scratch hardness of the coating film having a film thickness of 5 μm formed by the resin solution was 8H.

(3-4) Example 4
The BN core was immersed in a resin solution having the following composition, then taken out, and the solvent was dried to form a coating layer having a film thickness of about 1 μm on the surface.
Organic Inorganic Hybrid Resin (Composelan E203, Silica / Epoxy Hybrid Resin, Arakawa Chemical): 15% by weight
Pigment color material (MHI red, Mikuni color): 60% by weight
Antistatic agent (HICERA, Miyazaki Chemical): 3% by weight
Organic solvent (isopropyl alcohol): 22% by weight
The scratch hardness of the coating film having a film thickness of 5 μm formed by the resin solution was 8H.

(3-5) Example 5
The BN core was immersed in a resin solution having the following composition, then taken out, and the solvent was dried to form a coating layer having a film thickness of about 1 μm on the surface.
Epoxy resin (825, Mitsubishi Chemical): 15% by weight
Organic solvent (isopropyl alcohol): 85% by weight
The scratch hardness of the coating film having a film thickness of 5 μm formed by the resin solution was 3H.

(3-6) Example 6
The BN core was immersed in a resin solution having the following composition, then taken out, and the solvent was dried to form a coating layer having a film thickness of about 1 μm on the surface.
Ketone resin (K-90, Arakawa Chemical): 15% by weight
Organic solvent (isopropyl alcohol): 85% by weight
The scratch hardness of the coating film having a film thickness of 5 μm formed by the resin solution was 3H.

(3-7) Example 7
The BN core was immersed in a resin solution having the following composition, then taken out, and the solvent was dried to form a coating layer having a film thickness of about 1 μm on the surface.
Urea resin (Flaamine, Daiwa Co., Ltd.): 15% by weight
Organic solvent (isopropyl alcohol): 85% by weight
The scratch hardness of the coating film having a film thickness of 5 μm formed by the resin solution was 3H.

(3-8) Example 8
The BN core was immersed in a resin solution having the following composition, then taken out, and the solvent was dried to form a coating layer having a film thickness of about 1 μm on the surface.
Fluororesin (FG-5040, Fluoro Technology Co., Ltd.): 15% by weight
Organic solvent (isopropyl alcohol): 85% by weight
The scratch hardness of the coating film having a film thickness of 5 μm formed by the resin solution was 3H.

(3-9) Example 9
The BN core was immersed in a resin solution having the following composition, then taken out, and the solvent was dried to form a coating layer having a film thickness of about 1 μm on the surface.
Silicone resin (MRS-102, Yoshida KSK): 15% by weight
Organic solvent (isopropyl alcohol): 85% by weight
The scratch hardness of the coating film having a film thickness of 5 μm formed by the resin solution was 3H.

(3-10) Example 10
The BN core was immersed in a resin solution having the following composition, then taken out, and the solvent was dried to form a coating layer having a film thickness of about 1 μm on the surface.
Acrylic resin (A-198-XB, DIC): 15% by weight
Organic solvent (isopropyl alcohol): 85% by weight
The scratch hardness of the coating film having a film thickness of 5 μm formed by the resin solution was 3H.

(3-11) Example 11
The graphite core was immersed in a resin solution having the following composition, then taken out, and the solvent was dried to form a coating layer having a film thickness of about 1 μm on the surface.
Organic Inorganic Hybrid Resin (Composelan E203, Silica / Epoxy Hybrid Resin, Arakawa Chemical): 15% by weight
Pigment color material (MHI red, Mikuni color): 60% by weight
Organic solvent (isopropyl alcohol): 25% by weight
The scratch hardness of the coating film having a film thickness of 5 μm formed by the resin solution was 8H.

(4) Comparative Example (4-1) Comparative Example 1
The BN core was used as it was.

(4-2) Comparative Example 2
The BN core was immersed in a resin solution having the following composition, then taken out, and the solvent was dried to form a coating layer having a film thickness of about 1 μm on the surface.
Silicone resin (805 resin, Toray Dow Corning): 15% by weight
Organic solvent (isopropyl alcohol): 85% by weight
The scratch hardness of the coating film having a film thickness of 5 μm formed by the resin solution was B.

(4-3) Comparative Example 3
The graphite core was used as it was.

(5) Test method (5-1) Strength test Bending strength (unit: MPa) was measured for every 100 samples in accordance with JIS S 6005: 2007, and the average was calculated.

(5-2) Chuck holding force test Pull out the lead while it is set on the mechanical pencil, stand the mechanical pencil vertically on the writing surface while holding it on the chuck, apply force vertically downward, and dive into the lead (the lead is pushed back). The force (unit: N) when the pencil occurred was measured. This measurement was performed immediately after the core was set and after knocking 10,000 times with the core set.

(5-3) Light resistance test Cover the lower half of the core with aluminum foil so that it is not exposed, set it in a light resistance test fade meter (Suga Test Instruments Co., Ltd., X25), expose it for 100 hours, and then the exposed part is aluminum. It was visually confirmed whether the color faded and the color changed with respect to the part covered with the foil. The evaluation criteria were "A" when there was almost no change in color, and "B" when there was a change in color due to fading.

(5-4) Charging performance test With 20 cores in a case, the cells were allowed to stand in a room at a temperature of 25 ° C. and a humidity of 10% for one day. After that, the case was shaken at a speed of about twice a second for 1 minute, the lid of the case was opened, the case was tilted so that the lid side was directly below, and the number of the cores that had fallen was counted. The evaluation standard was "A" when the number of dropped cores was 10 or more, and "B" when the number of dropped cores was 9 or less.

(6) Test results The results of each test in (5) above are shown in Table 1 below. In addition, "-" in the table indicates that the resin type and scratch hardness are not coated with the resin, and the light resistance and the electric resistance performance are not tested.

(6-1) BN core Regarding the BN core, the bending strength and the chuck holding force are excellent in all of Examples 1 to 10 in which the coating layer is formed, as opposed to Comparative Example 1 in which the coating layer is not formed. rice field.
Further, as opposed to Comparative Example 2 in which the coating layer is formed of a resin having a scratch hardness lower than HB due to different resin products, Example 1 in which the coating layer is formed of a resin having a scratch hardness of HB or higher. ~ 10 had excellent bending strength.
Among Examples 1 to 10, Examples 1 to 4, which have a relatively high scratch hardness of 8H, have excellent bending strength as compared with Examples 5 to 10, which have a relatively low scratch hardness of 3H. Was there.
In Examples 2 and 4 in which the pigment coloring material is added to the coating layer, and Example 3 in which the ultraviolet absorber is added, neither the pigment coloring material nor the ultraviolet absorber is added. It has excellent light resistance as compared with Examples 1 and 5 to 10, and can be expected to prevent the core color from fading over time.
Furthermore, from the results of Example 4, an antistatic effect can be expected by adding an antistatic agent to the coating layer.

(6-2) Graphite core As for the graphite core, the bending strength and the chuck holding force were excellent in Example 11 in which the coating layer was formed, as compared with Comparative Example 3 in which the coating layer was not formed. Although it is not directly related to the light resistance, in Example 11, a coloring material can be added to express a red color different from the black color of the core color on the core surface, thereby improving the design. can.

The present invention can be used for pencil leads and mechanical pencil leads.

Claims (5)

A pencil lead in which the surface of a porous fired core containing only boron nitride is coated with a resin coating layer.
A pencil with the tip of the core left in a cylindrical shape and the tip of which is sharpened to a flat surface is pressed against the surface of a horizontal flat plate coated with the test resin with a thickness of 5 μm at a load of 7.355 N at a 45 ° angle. When the hardness of the pencil with the softest core that causes indentations on the surface when scratched is defined as the scratch hardness of the test resin,
The scratch hardness of the resin constituting the coating layer is 3H or more, and the scratch hardness is 3H or more .
The resin is a pencil lead selected from the group consisting of an organic-inorganic hybrid resin, a ketone resin, an acrylic resin, a urea resin, an epoxy resin, a silicone resin and a fluororesin . A pencil lead in which the surface of a black fired core made of graphite and binder carbon is coated with a resin coating layer.
A pencil with the tip of the core left in a cylindrical shape and the tip of which is sharpened to a flat surface is pressed against the surface of a horizontal flat plate coated with the test resin with a thickness of 5 μm at a load of 7.355 N at a 45 ° angle. When the hardness of the pencil with the softest core that causes indentations on the surface when scratched is defined as the scratch hardness of the test resin,
The scratch hardness of the resin constituting the coating layer is 3H or more, and the scratch hardness is 3H or more.
The resin is a pencil lead selected from the group consisting of an organic-inorganic hybrid resin , a ketone resin , an acrylic resin, a urea resin , an epoxy resin, a silicone resin , and a fluororesin. The pencil lead according to claim 1 or 2, wherein the coating layer further contains a coloring material. The pencil lead according to claim 1 or 2, wherein the coating layer further contains an ultraviolet absorber. The pencil lead according to claim 1 or 2, wherein the coating layer further contains an antistatic agent.

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